Suggestions for a good primer on Evolution?

Does anyone know of a good, simple, clear, not-TOO-dense book explaining evolution? I'm asking for something somewhat contradictory but I'm trying to find a good balance of depth, necessary detail, and support mixed with clarity, simplicity, and the assumption of both a lack of a scientific background as well as the lack (in general) of scientific (to the reader) minutae.

Basically I'm trying to find a Primer of sorts for somewhat openminded theists. I know quite a few culturally religious co-workers who would be open to learning a bit more about the subject but are turned off by works that are either too dense and imposing (they don't want to feel like they're reading a school textbook), or too ephemeral and general, dealing with only concepts but no backing. I'm trying to find something that addresses the middleground well with a clear general overview, the first few steps along the path of "good scientific backup" where they can then pick up more detailed books if they choose.

Something to interest and get the idea across without drowning them when they take their first dip in the pool ;) I was thinking 50-100 pages at most would probably be a good limiter as well.

I appreciate it but they're not interested enough to bother. I'm talking about a 30-40 year old, 30k/yr office worker in the south with no education beyond high school, 3 kids, and little time.

If it's not short, it won't even be picked up. If it's not simple, it'll be put down as "Gah, what am I taking a university class?? It feels like this is a textbook and there'll be a test next week". There not a lot of foundation to build on but they are casually interested about "Why you are so certain this is right, because, I mean, if we came from monkeys like it says there'd be no monkey's, right? So doesn't that pretty much show it's not true?" They're asking, not stating, they're curious, but not enough so to wade through 400 pages ;)